1. Field of the Invention
The present invention relates to an image processing technique for reading image information of an original document.
2. Description of the Related Art
A demand for high-resolution color image information is growing along with advances in communication networks, and widespread use of high-speed computers and high capacity storage media. In particular, there is a strong demand for a scanner that reads color image with high precision, high speed and high quality.
There is also a demand for quickly reading an image on a photographic film, such as a sleeve film having a plurality frames, at a high image quality. Japanese Patent Laid-Open No. 2001-298593 (corresponding U.S. Pat. No. 6,660,987) discloses an image reader for removing scratch and dirt on a film to read a high-quality image. According to the disclosure, the image reader includes an infrared light-emitting diode (LED) for detecting scratch and dirt and a planar light source having a light source for reading images. Images are thus read with scratch and dirt information removed therefrom.
The image reader 1 of FIG. 2 disclosed in Japanese Patent Laid-Open No. 2001-298593 reads original document images and photographic film images.
The image reader 1 includes a transmissive original document illumination device 2 for reading a photographic film 20. An image reader control board 3 is electrically connected to the transmissive original document illumination device 2 through a transmissive original document light source inverter 4 and an interface cable 5 to control the transmissive original document illumination device 2. As shown in FIG. 2, the image reader 1 also includes a transmissive original document light source 6 for directing visible light and infrared light to the transmissive original document.
An optical unit 15 focuses an image of an original document on a charge-coupled device (CCD) image sensor 7. The optical unit 15 includes a first reflective mirror 8, a second reflective mirror 9, a third reflective mirror 10, a fourth reflective mirror 11, a fifth reflective mirror 12, a lens 13, a visible-light path length correction glass 21, and a reflective original document illumination light source 14 for illuminating the original document. The optical unit 15 reads the image while being moved in a sub-scan direction as shown by a motor 17. The motor 17 is electrically connected to the image reader control board 3 via a signal cable 16. When placed in a lying position, the visible-light path length correction glass 21 is retraced from the optical path. When placed in an upright position, the visible-light path length correction glass 21 is inserted in the optical path. The CCD image sensor 7 is electrically connected to the image reader control board 3 through a signal cable 18. The motor 17 drives the optical unit 15 in a sub-scan direction. The image reader control board 3 is also connected to an external interface 19. Through the external interface 19, the image reader control board 3 is controlled from the outside. An electrical signal into which the CCD image sensor 7 has photoelectrically converted the optical image of the original document is thus outputted to the outside.
To detect the scratch and dirt information of the film original document 20, the transmissive original document light source 6 emits infrared light. The visible-light path length correction glass 21 is set to an upright position to adjust the optical length so that infrared light is focused on the surface of a film original document sheet. The image reader control board 3 controls the optical unit 15, thereby causing infrared light to scan the film original document. Image data is thus obtained. Film original document sheets typically allow infrared light to transmit therethrough while a scratch and dirt affected area blocks infrared light. By examining luminance on the image data, the scratch and dirt information is obtained.
However, the image reader requires the infrared light source in addition to the transmissive original document illumination light source 6, and further correction means for correcting the optical paths of visible light and infrared light. As such, the structure and control of the image reader become complex.